Vinyl sulfonic acids are attracting a great deal of attention as a monomer for constituting a functional polymer and a conductive material.
However, commercially available vinyl sulfonic acids have a double bond content of 75 wt. % or less. Consequently, when the vinyl sulfonic acid was to be polymerized after impregnating in a porous substrate, polymerization did not proceed sufficiently and thus a product functioning as a proton conductive polymer could not be obtained.
Patent Document 1 describes a vinyl sulfonic acid with a purity of 98%. However, the metal content is several ppm.
Recently, vinyl sulfonic acids or polymers thereof are attracting attention as a component constituting functional polymers and conductive materials, and as a material for electronic devices and semiconductors.
For example, a vinyl sulfonic acid or polymer thereof has been reported as being utilized in a resist resin composition (Patent Document 2), a resin composition for a resist protection film (Patent Documents 3 and 4), a CMP slurry (Patent Documents 5 and 6), a separator for an alkali secondary battery (Patent Documents 7 and 8), a fuel cell electrolyte membrane (Patent Documents 1 and 9), a conductive polymer dopant (Patent Documents 10 and 11) and the like.
Patent Document 1: WO 2006/059582
Patent Document 2: Japanese Patent Laid-Open No. 2000-035672
Patent Document 3: Japanese Patent Laid-Open No. 10-120968
Patent Document 4: Japanese Patent Laid-Open No. 2006-259382
Patent Document 5: Japanese Patent Laid-Open No. 2004
Patent Document 6: Japanese Patent Laid-Open No. 2006-179678
Patent Document 7: Japanese Patent Laid-Open No. 2000-195489
Patent Document 8: Japanese Patent Laid-Open No. 2003-031198
Patent Document 9: Japanese Patent No. 4048063
Patent Document 10: National Publication of International Patent Application No. 2005-536595
Patent Document 11: Japanese Patent Laid-Open No. 2005-190940
However, many of these uses dislike metal or impurity contamination.
For example, for a semiconductor material, impurities, especially metal impurities contained in the material, can cause problems such as contamination of the wafer by diffusing into the wafer interior during the wafer fabrication step. Further, metal contamination can induce deteriorated reliability of the dielectric film, current leakage, and abnormalities in film deposition and the like, and also have an substantial adverse impact on the semiconductor apparatus (see Patent Documents 12 to 14).
Patent Document 12: Japanese Patent Laid-Open No. 2007-150153
Patent Document 13: Japanese Patent Laid-Open No. 2004-189820
Patent Document 14: Japanese Patent Laid-Open No. 2001-250807
Further, recently, from the perspectives that solid polymer fuel cells utilizing a polymer electrolyte membrane have a light burden on the environment and reduced carbon dioxide emissions, investigations are being carried out on their various applications, such as for automobiles and fixed household use.
Conventionally, a perfluoroalkyl sulfonate-type polymer in which sulfonic acid groups are linked to side chains on a perfluoro skeleton has been used as such a polymer electrolyte membrane. Further, perfluoroalkyl sulfonate-type polymers which have undergone various improvements have been developed. However, since the polymer production process is complex, and a fluorinated hydrocarbon-based material, for which large cost reductions are not easy to achieve, is used, costs increase.
Accordingly, hydrocarbon-based polymer electrolyte membranes which do not use a fluorine-based polymer and which have improved proton conductivity have been developed. Hydrocarbon-based polymer electrolyte membranes are easy to produce, can be applied in a large variety of molecular structures, and have easily-controlled physical properties. Further, from a recycling perspective, since hydrocarbon-based polymer electrolyte membranes do not contain a fluorine, they have the advantage of not producing harmful substances.
However, hydrocarbon-based polymers have worse chemical stability than perfluoroalkyl sulfonate-type polymers. This is due to the fact that hydrogen and oxygen crossleak across the electrolyte membrane and react on the electrode catalyst to produce hydrogen peroxide, whereby radicals produced from this hydrogen peroxide cause the membrane to deteriorate. Further, iron ions act as a catalyst for promoting the oxidation ability of the hydrogen peroxide, so that the membrane deterioration is accelerated (see Non-Patent Document 1).
Non-Patent Document 1: Fuel Cell Technology and Applications/Handbook of Fuel Cells, pp. 647-662, 2003
However, a vinyl sulfonic acid or polymer thereof having a sufficiently reduced metal content is as yet unknown.
On the other hand, various methods are known for producing a vinyl sulfonic acid (see Non-Patent Document 2). For example, Patent Document 15 describes a method for producing a vinyl sulfonic acid by performing a sodium removal treatment on sodium vinyl sulfonate with hydrochloric acid.
Further, Patent Document 16 describes a method for producing a vinyl sulfonic acid by dehydrating isethionic acid using diphosphate pentoxide or pyrophosphoric acid as a dehydrating agent.
However, in the above-described methods, a product having sufficient quality cannot be obtained.
Non-Patent Document 2: Sango Kunichika, Takao Katagiri, Journal of the Chemical Society of Japan, Industrial chemistry section Vol. 64, No. 5, 1961, pp. 929-932
Patent Document 15: U.S. Pat. No. 3,312,735
Patent Document 16: U.S. Pat. No. 2,597,696